The primary objective of this proposal is to assess the hazard to human health represented by selected chemicals distributed in the environment. This involves two secondary objectives: (1) Definition of the frequency, extent and route of human exposure to such chemicals. This requires a study of those factors influencing the release, distribution and modification of a chemical in the environment and subsequent definition of primary and secondary routes of entry into humans and food animals. (2) The biological response produced by these chemicals must be determined or reliably projected for exposure levels which might be found in the environment. To accomplish this, studies must be made at all levels of biological organization and an assessment of the true significance of observed effects must be made.